Although it is acknowledged that postembryonic development in insects is under neuroendocrine control, the basic endocrinology of the principal neurohormone involved, the prothoracicotropic hormone (PTTH), has not been elucidated. The paucity of information on PTTH has been due in part to the lack of an adequate assay for this neuropeptide hormone. This laboratory has recently developed a quantitative in vitro assay for PTTH which has overcome this limitation, measuring in vitro activation of a target gland by PTTH. With this assay, a study can now be made of the basic endocrinology and the chemical nature of this neurohormone. The primary focus of this proposal is the chemical characterization of PTTH. At present, there appear to be two molecular forms of the hormone, one possibly being a glycopeptide. The kinetics of prothoracic gland activation by each form is different, suggesting different functions and different mechanisms of action. These two forms will be purified and then sequenced. The glycopeptide form of PTTH will be characterized by chemical analysis of neutral sugar constituents, radiosynthesis and affinity chromatography. With purified hormone(s), an antibody(s) will then be generated for the development of a PTTH RIA and immunocytochemical studies initiated. The form of the hormone in the blood of the insect will be characterized as well. The basic endocrinology of the PTTH to be elucidated includes identification of the cerebral neurosecretory cell (NSC) that synthesizes the hormone, the site of its release and its titers in the brain and blood during development. Based upon progress to date, it appears that a single NSC in each hemisphere of the brain synthesizes PTTH and the site of its release is a structure peripheral to the brain (corpus allatum). These findings have established the boundaries of a unicellular neuroendocrine system with which it becomes possible to probe the synthesis, transport, release, etc. of a defined neuropeptide hormone at the level of the NSC. The biomedical potential of such a system for elucidating basic aspects of neuropeptide endocrinology in general is significant. In addition, the possible existence of multiple forms of PTTH may be helpful in establishing whether different forms of a neurohormone have distinct endocrine functions.